While many people consider psoriasis a skin disease, its primary cause is a malfunctioning immune system. And it doesn't just affect the skin. Many of its worst effects can come from psoriatic arthritis, a swelling of the joints that develops in some people with psoriasis. Psoriatic arthritis causes symptoms like other types of arthritis -- stiff, painful, and swollen joints -- and it can be serious. Untreated, psoriatic arthritis can cause bone loss and deformation of the joints.
Inflammation of tendon and their attachments to bone
How Psoriasis and Psoriatic Arthritis Are Connected
About 30% of people who have psoriasis will develop psoriatic arthritis. In most cases, the skin symptoms of psoriasis appear before psoriatic arthritis develops.
But sometimes psoriatic arthritis symptoms appear months, or even years, before skin lesions develop. In this circumstance it is often difficult to make a diagnosis.
Both psoriasis and psoriatic arthritis are thought to be related to problems with your immune system. As a result, your skin cells grow too quickly without sloughing off. Layers of skin build up, resulting in the skin plaques of psoriasis.
If you have psoriatic arthritis, your immune system targets your joints and connective tissue. This leads to:
Painful, swollen joints
Tendon attachments to bone (enthesopathy)
There's no connection between the location of your scaly skin patches from psoriasis and which joints are affected by psoriatic arthritis. For example, you could have situations like these:
Skin lesions on your elbows but NO psoriatic arthritis in the elbow joints.
Swelling of the toes from psoriatic arthritis but NO redness or scaling on the feet.
Psoriasis skin lesions can flare up and then get better. Psoriatic arthritis symptoms may also come and go.
Psoriasis does not cause scarring or any other permanent damage to the skin. But psoriatic arthritis can cause permanent deformity and damage to the joints if not treated. That's why it is very important to work with your doctor even if your psoriatic arthritis symptoms ease. Don't taper your medications without talking to your doctor first.
Psoriasis and psoriatic arthritis share a genetic link. Often there is a family history of either condition. About 40% of people who develop psoriatic arthritis have relatives with either psoriasis or psoriatic arthritis.
Scientists don't yet know which genes are responsible for psoriasis and psoriatic arthritis. Studies are underway to find genetic markers.
Discovering which genes are involved in psoriatic arthritis may help lead to new treatments. Currently it isn't possible to predict which people with psoriasis will go on to develop psoriatic arthritis.